PIC16LCR66T-10/SP View Datasheet(PDF) - Microchip Technology
Part Name
Description
Manufacturer
PIC16LCR66T-10/SP Datasheet PDF : 336 Pages
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7.0 TIMER0 MODULE
Applicable Devices
61 62 62A R62 63 R63 64 64A R64 65 65A R65 66 67
The Timer0 module has the following features:
• 8-bit timer/counter register, TMR0
- Read and write capability
- Interrupt on overflow from FFh to 00h
• 8-bit software programmable prescaler
• Internal or external clock select
- Edge select for external clock
Figure 7-1 is a simplified block diagram of the Timer0
module.
Timer mode is selected by clearing bit T0CS
(OPTION<5>). In timer mode, the Timer0 module will
increment every instruction cycle (without prescaler). If
TMR0 register is written, the increment is inhibited for
the following two instruction cycles (Figure 7-2 and
Figure 7-3). The user can work around this by writing
an adjusted value to the TMR0 register.
Counter mode is selected by setting bit T0CS. In this
mode, Timer0 will increment either on every rising or
falling edge of pin RA4/T0CKI. The incrementing edge
is determined by the source edge select bit T0SE
PIC16C6X
(OPTION<4>). Clearing bit T0SE selects the rising
edge. Restrictions on the external clock input are dis-
cussed in detail in Section 7.2.
The prescaler is mutually exclusively shared between
the Timer0 module and the Watchdog Timer. The pres-
caler assignment is controlled in software by control bit
PSA (OPTION<3>). Clearing bit PSA will assign the
prescaler to the Timer0 module. The prescaler is not
readable or writable. When the prescaler is assigned to
the Timer0 module, prescale values of 1:2, 1:4, ...,
1:256 are selectable. Section 7.3 details the operation
of the prescaler.
7.1 TMR0 Interrupt
Applicable Devices
61 62 62A R62 63 R63 64 64A R64 65 65A R65 66 67
The TMR0 interrupt is generated when the register
(TMR0) overflows from FFh to 00h. This overflow sets
interrupt flag bit T0IF (INTCON<2>). The interrupt can
be masked by clearing enable bit T0IE (INTCON<5>).
Flag bit T0IF must be cleared in software by the TImer0
interrupt service routine before re-enabling this inter-
rupt. The TMR0 interrupt cannot wake the processor
from SLEEP since the timer is shut off during SLEEP.
Figure 7-4 displays the Timer0 interrupt timing.
FIGURE 7-1: TIMER0 BLOCK DIAGRAM
RA4/T0CKI FOSC/4
pin
T0SE
0
1
T0CS
Programmable
Prescaler
3
PS2, PS1, PS0
Data bus
PSout
1
0
Sync with
Internal
clocks
PSout
(2 cycle delay)
8
TMR0 reg
PSA
Set bit T0IF
on overflow
Note 1: Bits, T0CS, T0SE, PSA, and PS2, PS1, PS0 are (OPTION<5:0).
2: The prescaler is shared with Watchdog Timer (refer to Figure 7-6 for detailed diagram).
FIGURE 7-2: TIMER0 TIMING: INTERNAL CLOCK/NO PRESCALER
PC
(Program
Counter)
Instruction
Fetch
Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4
PC-1
PC
PC+1
PC+2
PC+3
PC+4
PC+5
MOVWF TMR0 MOVF TMR0,W MOVF TMR0,W MOVF TMR0,W MOVF TMR0,W MOVF TMR0,W
PC+6
TMR0
T0
Instruction
Executed
T0+1
T0+2
NT0
NT0
NT0
NT0+1
NT0+2
Write TMR0
executed
Read TMR0
reads NT0
Read TMR0
reads NT0
Read TMR0
reads NT0
Read TMR0
Read TMR0
reads NT0 + 1 reads NT0 + 2
© 1997 Microchip Technology Inc.
DS30234D-page 65
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